Biomedical Instrumentation .


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Biomedical Instrumentation. Chapter 6 in Introduction to Biomedical Equipment Technology By Joseph Carr and John Brown. Signal Acquisition.
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Biomedical Instrumentation Chapter 6 in Introduction to Biomedical Equipment Technology By Joseph Carr and John Brown

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Signal Acquisition Medical Instrumentation normally involves checking a flag off the body which is simple, changing over it to an electrical flag, and digitizing it to be broke down by the PC.

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Types of Sensors: Electrodes: obtain an electrical flag Transducers: procure a non-electrical flag (drive, weight, temp and so forth) and proselytes it to an electrical flag

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Active versus Passive Sensors: Active Sensor: Requires an outside AC or DC electrical source to control the gadget Strain gage, pulse sensor Passive Sensor: Provides it possess vitality or gets vitality from wonder being considered Thermocouple

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Sensor Error Sources Error: Difference between measured esteem and genuine esteem.

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5 Categories of Errors: Insertion Error Application Error Characteristic Error Dynamic Error Environmental Error

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Insertion Error: Error happening while embeddings a sensor

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Application Error: Errors brought on by Operator

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Characteristic Error: Errors inalienable to Device

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Dynamic Error: Most instruments are aligned in static conditions on the off chance that you are perusing a thermistor it requires investment to change its esteem. In the event that you read this esteem to rapidly a mistake will come about.

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Environmental Error: Errors brought on by environment warm, mugginess

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Sensor Terminology Sensitivity : Slope of yield trademark bend Δy/Δx; Minimum contribution of physical parameter will make a perceptible yield change Blood weight transducer may have an affectability of 10 uV/V/mmHg so you will see a 10 uV change for each V or mmHg connected to the framework.

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Output Input Which is more delicate? The left side one since you\'ll have a bigger change in y for a given change in x

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Ideal Curve Output Input Sensitivity Error Sensor Terminology Sensitivity Error = Departure from perfect slant of a trademark bend

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Sensor Terminology Range = Maximum and Minimum estimations of connected parameter that can be measured. In the event that an instrument can read up to 200 mmHg and the genuine perusing is 250 mmHg then you have surpassed the scope of the instrument.

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Sensor Terminology Dynamic Range: add up to scope of sensor for least to most extreme. Ie if your instrument can gauge from - 10V to +10 V your dynamic range is 20V Precision = Degree of reproducibility signified as the scope of one standard deviation σ Resolution = littlest discernible incremental change of information parameter that can be recognized

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Xi Xo Accuracy = most extreme contrast that will exist between the genuine esteem and the demonstrated estimation of the sensor

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Offset Error Offset mistake = yield that will exist when it ought to be zero The trademark bend had similar touchy slant yet had a y block Output Input Offset Error Zero counterbalance blunder

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Linearity = Extent to which real quantify bended or adjustment bend leaves from perfect bend.

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Full Scale Input Ideal Measure Output Din(Max) Input Linearity Nonlinearity (%) = (Din(Max)/INfs) * 100% Nonlinearity is rate of nonlinear Din(max) = greatest info deviation INfs = most extreme full-scale input

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Hysteresis = estimation of how sensor changes with information parameter in light of heading of progress

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Output = F(x) P F2 Input = x F1 B Q Hysteresis The esteem B can be spoken to by 2 estimations of F(x), F1 and F2. On the off chance that you are at point P then you achieve B by the esteem F2. In the event that you are at point Q then you achieve B by estimation of F1.

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F(t) Tolerance Band Tresponse 100% 70% Rising Response Time Ton Response Time Response Time: Time required for a sensor yield to change from past state to definite settle esteem inside a resilience band of right new esteem signified in red can be distinctive in rising and rotting headings

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F(t) Tolerance Band Tresponse 100% 70% Rising Response Time Ton Response Time Constant: Depending on the source is characterized as the measure of time to achieve 0% to 70% of conclusive esteem. Ordinarily meant for capacitors as T = R C (Resistance * Capacitance) signified in Blue

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Response Time Convergence Eye Movement the internal turning of the eyes have an alternate reaction time than dissimilarity eye developments the outward turning of the eyes which would be the rot reaction time Tdecay F(t) Decaying Response Time Toff Time

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F(x)* = hatchet + bx 2 +cx 4 + . . . +K F(x)* = hatchet + bx 3 +cx 5 + . . . +K Output F(x) Output F(x) F(x) = mx + K F(x) = mx + K Input X Input X Dynamic Linearity Measure of a sensor\'s capacity to take after fast changes in the information parameters. Contrast amongst strong and dashed bends is the non-linearity as portrayed by the higher request x terms

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Asymmetric = F(x) != |F(- x)| where F(x)* is topsy-turvy around straight bend F(x) then F(x) = hatchet + bx 2 +cx 4 + . . . +K balancing for K or you could accept K = 0 Symmetrical = F(x) = |F(- x)| where F(x) * is symmetric around straight bend F(x) then F(x) = hatchet +bx 3 + cx 5 +. . . + K balancing for K or you could accept K =0 Dynamic Linearity

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Av = Vo/Vi 1.0 Frequency ( w ) radians every second Frequency Response of Ideal and Practical System When you take a gander at the recurrence reaction of an instrument, in a perfect world you need a wideband level recurrence reaction.

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Av = Vo/Vi 1.0 0.707 FL FH Frequency ( w ) radians every second Frequency Response of Ideal and Practical System by and by, you have weakening of lower and higher frequencies FL and FH are known as the –3 dB focuses in voltage frameworks.

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Examples of Filters Ideal Filter has sharp shorts and a level pass band Most channels lessen upper and lower frequencies Other channels constrict upper and lower frequencies and are not level in the pass band

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Electrodes for Biophysical Sensing Bioelectricity: actually happening current that exists since living beings have particles in different amounts

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Electrodes for Biophysical Sensing Ionic Conduction: Migration of particles decidedly and contrarily charge atoms all through an area. To a great degree nonlinear yet in the event that you restrain the area can be viewed as straight

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Electrodes for Biophysical Sensing Electronic Conduction: Flow of electrons affected by an electrical field

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Bioelectrodes: class of sensors that transduce ionic conduction to electronic conduction so can handle by electric circuits Used to obtain ECG, EEG, EMG, and so forth

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Bioelectrodes 3 Types of cathodes: Surface (in vivo) outside body Indwelling Macroelectrodes (in vivo) Microelectrodes (in vitro) inside body

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Bioelectrodes Electrode Potentials: Skin is electrolytic and can be displayed as electrolytic arrangements Metal Electrode Electrolytic Solution where Skin is electrolytic and can be demonstrated as saline

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Electrodes in Solution Have metallic anode submerged in electrolytic arrangement once metal test is in electrolytic arrangement it: Discharges metallic particles into arrangement Some particles in arrangement join with metallic terminals Charge slope constructs making a potential distinction or you have a cathode potential or ½ cell potential

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Electrodes in Solution 2 cells An and B, A has 2 positive particles And B has 3 positive particles subsequently have a Potential contrast of 3 –2 = 1 where B is more positive than An A ++ B +++

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Electrodes Two responses occur at terminal/electrolyte interface: Oxidizing Reaction: Metal - > electrons + metal particles Reduction Reaction : Electrons + metal particles - > Metal

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Vae Metal A Vbe Metal B Electrolytic Solution Electrodes Electrode Double Layer: framed by 2 parallel layers of particles of inverse charge brought about by particles relocating from 1 side of locale or another; ionic contrasts are the wellspring of the cathode potential or half-cell potential (Ve).

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Electrodes If metals are diverse you will have differential potential some of the time called a terminal counterbalance potential. Metal A = gold Vae = 1.50V and Metal B = silver Vbe = 0.8V then Vab = 1.5V – 0.8 V = 0.7V (Table 6-1 in book page 96) Vae Metal A Vbe Metal B Electrolytic Solution

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Electrodes Two general classifications of material mixes: Perfectly energized or flawlessly nonreversible cathode: no net exchange of charge crosswise over metal/electrolyte interface Perfectly Nonpolarized or splendidly reversible terminal: unhindered exchange of charge between metal anode and the cathode Generally select a reversible cathode, for example, Ag-AgCl (silver-silver chloride)

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R t = inner resistance of body which is low Vd = Differential voltage Vd Rsa and Rsb = skin resistance at terminal An and B Electrode A C1a Vea + - Rsa Cellular Resistance R1a Rc - Vo Mass Tissue Resistance R t Vd Cellular Potentials + Electrode B C1b Veb + - Rsb R1b Ionic Conduction Electronic Conduction R1A and R1B = resistance of cathodes C1A and C1B = capacitance of terminals

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Electrode Potentials cause recording Problems ½ cell potential ~ 1.5 V while biopotentials are typically 1000 times less (ECG = 1-2 mV and EEG is 50 uV) in this way have a gigantic contrast between DC cell potential and biopotential Strategies to conquer DC part Differential DC speaker to get flag hence the DC segment will counteract Counter Offset-Voltage to wipe out half-cell potential AC couple contribution of enhancer (DC won\'t go through) ie capacitively couple the flag into the circuit

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Electrode Potentials make recording Problems Strategies beat DC segment Differential DC intensifier to obtain flag th

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